Which one of the following forces is a contact force?
(a) force of gravity (c) magnetic force
(b) force of friction (d) electrostatic force
Two objects repel each other. This repulsion could be due to
(a) frictional force only
(b) electrostatic force only
(c) magnetic force only
(d) either a magnetic or an electrostatic force
During dry weather, while combing hair, sometimes we experience hair flying apart. The force responsible for this is
(a) force of gravity. (c) force of friction. (b) electrostatic force. (d) magnetic force
It is believed that height of a child depends upon the genes
inherited from parents. However, it is often seen that tall parents
may have short children and vice-versa. Are there factors other
than genes, that can cause these variations?
Our government has legalised the age for marriage in boys and
girls. Give reasons as to why one should get married after a
certain age.
Salma had a very soft and smooth skin during her childhood.
As she entered adolescence, she developed pimples on her face.
The skin specialist advised her to wash her face at regular
intervals. Can you explain the reasons for the appearance of
pimples on her face and suggest ways to prevent them?
John and Radha were classmates since childhood. When Radha
became eleven years old, she developed a little swelling on her
neck. She visited the doctor who started medication for her. After
a few years, John also developed a slight protrusion on his throat.
He got worried and went to the doctor. But, the doctor assured
him that it was a normal feature in boys while they are growing
up. Can you think of any reasons for the difference in diagnoses?
In human females, each time during maturation and release of egg the inner wall of uterus thickens. Is this thickening permanent? Give reasons.
Name the hormone which would be released during the following situations:
(a) a frightened person.
(b) growth of a child to adult.
(c) development of caterpillar to moth.
(d) development of tadpole to frog.
During adolescence, the body of boys and girls undergoes certain changes. Given below are a few of those changes.
(a) Broad shoulders
(b) Wider chests
(c) Wider region below waist
(d) Development of muscles
(e) Development of mammary glands
(f) Growth of facial hair
(g) Acne and pimples on face
(h) Development of sex organs
(i) High-pitched voice
(j) Growth of pubic hair.
Categorise these changes into those that occur in boys and those that occur in girls and fill in the table given below.
Body changes during Adolescence
Boys Girls
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